unittest: tearDown is not called if asyncSetUp fails

In unittest.TestCase, tearDown() is always called if setUp() is successful. It is only not called when setUp() fails. In IsolatedAsyncioTestCase, which is a subclass of TestCase, tearDown() is not called if setUp() is successful, but asyncSetUp() fails. I think is a problem.

Linked PRs

• gh-99596

首先比較 unittest.TestCase 與 IsolatedAsyncioTestCase 的 setup 和 teardown 生命週期，著重於 asyncSetUp() 失敗時會發生什麼情況。連結的 PR gh-99596 所參照的工作應包括：在 setUp() 成功後接著 asyncSetUp() 失敗時執行 teardown，並提供回歸測試涵蓋。